A high-performance and compact image-sensing unit or camera such as a digital camera has an aspherical lens made of a high-refractivity glass. Such lenses are mass-produced by press-molding a glass material called a preform with a press mold having precision-worked molding surfaces to precisely transferring forms of the above molding surfaces to the glass material.
The above press-molding is called precision press-molding and capable of forming an optical-function surface of an optical element by press-molding, so that it enables the mass production of aspherical lenses at a low cost and with high productivity as compared with a process of completing aspherical lenses by grinding and polishing glass to lenses one after another.
There have been proposed precision press-molding glasses having various optical properties. Specifically, JP-A-6-305769 and JP-A-8-217484 proposes such glasses.